I've not found any solution. The guards made of mesh, plastic, metal, whatever, tend to get clogged if you have trees that drop small seeds. Cottonwood is a weed around here. In the spring, the cotton goes flying around. It is impossible to get out of the mesh. I tore those style of guards out after a few years. As well, small stuff from the shingles on our house could fall through the mesh. I found a half inch think layer of black gunk lying in the bottoms of our gutters in spots, since the mesh does not stop really small stuff.
The gutter caps have a reputation as hornet hotels. Wasps can build nests underneath them, and I have a known bee sting allergy.
My solution is a simple one. Clean out the gutters twice a year. I blow them out with a leaf blower, standing on the ground. I added a couple of pieces of pvc angle to my leaf blower, with a long extension. Then I put on a hooded jacket when the gutters are dry, and blow the mess out away from me if possible. I usually get a face full or two, but that is what the hooded jacket is for.
Neighbors of ours chose to skip gutters completely when they just built their new home. But that leaves you with a need to deal with water near your foundation.